Ca40(α,γ)Ti44Reaction in the Energy Regime of Supernova Nucleosynthesis

The {sup 44}Ti(t{sub 1/2}=59 yr) nuclide, an important signature of supernova nucleosynthesis, has recently been observed as live radioactivity by {gamma}-ray astronomy from the Cas A remnant. We investigate in the laboratory the major {sup 44}Ti production reaction {sup 40}Ca({alpha},{gamma}){sup 44}Ti (E{sub c.m.}{approx}0.6-1.2 MeV/u) by direct off-line counting of {sup 44}Ti nuclei. The yield, significantly higher than inferred from previous experiments, is analyzed in terms of a statistical model using microscopic nuclear inputs. The associated stellar rate has important astrophysical consequences, increasing the calculated supernova {sup 44}Ti yield by a factor {approx}2 over previous estimates and bringing it closer to Cas A observations.